MORPHOLOGY OF MEMBERS. 
among Lycopodiaceae the genus Psilotum, among Orchideae Epipogum Gmelini and 
Corallorhiza innaia, are destitute of roots; the Httle Lemita {Wolffid) arrhiza does 
not form roots, and is at the same time destitute of vascular bundles. 
With reference to the place of their formation roots are remarkably variable. 
A root is usually present even in the young embryo which proceeds from the 
fertilised ovule (but not in Orchideae) ; it appears at the posterior end of the em- 
bryonal stem, and may be termed the Primary Root, whether it remains weakly 
and soon dies, as in Cryptogams and Monocotyledons^, or whether it continues 
to grow more vigorously, like the rest, as in many Dicotyledons. But besides the 
primary roots, there are usually formed in addition a large number of Secondary 
Roots, or simply Roots ; since they are enormously more numerous than the 
primary roots, and of much greater importance to the plant, a special name is 
superfluous where the contrast to the primary root is not of importance. They 
arise in the interior of the primary or secondary roots, and on stems and 
petioles. The primary root with its secondary roots, or any root with its lateral 
roots, may be termed a Root-system. With the exception of many Dicotyledons 
with a persistent strongly developed primary root, the majority of roots spring 
from stems, especially when these latter creep, float, climb, or form bulbs or tubers. 
In Tree-ferns the stem is often densely covered throughout its whole length with 
a felt of delicate roots. In Ferns with densely crowded leaves in which no portion 
of the surface of the stem is left bare, the roots spring exclusively from the 
petioles, as, for example, in Nephrodmm Fiiix-mas, Asptenium Filix-fcemina, Cera- 
topteris thatictroides, &c. ; sometimes the fronds put out roots as in Mertensia ^. 
When the stem possesses clearly developed nodes and internodes, the roots usually 
spring from the former ; thus, for example, exclusively from the nodes in Equise- 
taceae, and most commonly so in Grasses. 
Roots owe their origin either to the primary meristem, or to partially diff'erentiated 
masses of tissue, or finally to a secondary meristem enclosed between layers com- 
pletely differentiated. The primary roots of embryos arise from quite undifferentiated 
primary meristem ; the lateral roots of Cryptogams, as Nageli and Leitgeb have 
shown, originate near the growing point of roots, where the differentiation of their 
tissues first begins; and with Phanerogams the same is the case. But stems may 
also produce roots near their growing point, where the differentiation of the primary 
meristem first commences; this occurs in the case of the creeping stems of Rhizo- 
^ [On the primary root of Monocotyledons, which disappears at an early period, see Falkenberg, 
Vergleichende Untersuchungen über den Bau der Vegetationsorgane der Monocotyledonen. Stutt- 
gart 1876,] 
^ A leaf of Phaseolus multiflorus cut off at the pulvinus and placed in water developed from the 
callus an abundant root-system, and remained living for some months. [The leaves of Fims elastica 
behave in the same way.] According to Van Tieghem, the cotyledons of the sunflower, scarlet 
runner, Cucurbita maxima, Mirabilis Jalappa, &c., when laid on damp moss in a temperature of from 
22° to 25° C, produce in a few days a number of roots ; and this takes place even if the cotyledons 
are cut into small pieces, the roots then proceeding from the sections of the vascular bundles. I have 
myself seen a seedling of Cucurbita covered up too thickly with earth put forth long roots from its 
cotyledons. See further Dodel, Jahrb. für wiss. Bot. vol. VIII. p. 177. 
